In order to obtain information regarding temperature, density and other interior parameters of arbitrary objects without destroying, invading or dissecting the object, radiation(s) of various types are available to provide information that allow(s) to reconstruct the desired parameters.
Choosing a specific type of radiation, there are four distinct cases that incorporate their proper implications on the choice of method of analysis. These are classified by two question areas:                transparency of the object to the radiation chosen        resolution in the object required with respect to the wavelength of the chosen radiation.Case 1A        
(The object is transparent or weakly absorbing to the radiation used for measurement, and the resolution to be achieved is equal or smaller than a radiation wavelength).
The only source of information is obtained by probing the near field using e.g.                Atomic Force Microscopy (APM)                    reading out the force on a sub-wavelength-size stencil being positioned with high precision on the surface of a material reading out the structure on the surface of the object under test,                        Raster Tunnel Microscopy (RTM)                    where instead of the force one measures the tunneling current from a sub-wavelength sized probe being positioned close to the surface of the object under test generating information on the electronic state of the surface of the object, or                        optical Near Field Microscopy                    where electromagnetic radiation passes through microscopically small holes requiring the hole to be much smaller than a wavelength of the radiation used generating surface images of the optical properties at sub wavelength resolution on thin probes.                        Impedance tomography                    Where a set of electrodes is attached to the object under test and the impedance between all the probes is measured. This method allows calculating some properties of the interior of the object under test but resolution is generally poor. This method has been used with success in differential approaches—measuring the impedance of the cardiac region prior and after medication to evaluate the influence of, e.g. anti-clogging drugs.                        
As a general feature, the high resolution of the methods mentioned above are not due to the intrinsic wavelength of the chosen radiation but due to another constraint (mostly mechanical as diaphragms, stencils) that provides sub-wavelength resolution. A general shortcoming is given by the thickness requirement of the object under test—the above methods generate either only surface information or interior information at a very limited depth without losing resolution.
Case 1B
(The object is transparent or weakly absorbing to the radiation used for measurement, and the resolution is much larger than a radiation wavelength.)
This case is covered by all direct imaging and optical transmission methods. Using electromagnetic radiation in this regime, there are                LIDAR        X-ray        
As a means of analysis, ray tracing and one-to-one mapping methods are appropriate since scattering does not play a role—it can be assumed without loss of resolution that each pixel information taken at a given position is only affected by the object's volume located in between the radiation source and the receiver.
A recent development in this area is the passive radar where the thermal emission inherent to all bodies in the environment around a receiver is measured and imaged. This radar method does not require any transmitted signal and is therefore not traceable.
Among non-electromagnetic methods there are commercially available                Ultrasound tomography and        Nuclear Magnetic Resonance (NMR)Case 2A        
(The object is moderately absorbing to the radiation used for measurement, and the resolution is equal or smaller than a radiation wavelength).
The fact that the object is moderately absorbing to the radiation used for measurement puts a thickness limit to the probes that can be investigated.
For this case no feasible method is available today regarding the state of the art.
Case 2B
(The object is moderately absorbing to the radiation used for measurement, and the resolution is much larger than a radiation wavelength).
In this case, most radio frequency and microwave frequency applications are found (especially when the object under test is lossy and it is embedded in a non-lossy environment) and microwave tomography is available. Among these methods the most popular one is                (active) radio detection and ranging (RADAR)                    where the signal runtime between a source and a target and back to a receiver is measured either by putting the receiver at the same place as the transmitter (monostatic radar) or by putting the receiver at a different location than the transmitter (bistatic radar) and the frequency change due to the relative velocity of the source and target are evaluated (Doppler radar).                        
There is thus a need to develop an apparatus for determining physical parameters, such as temperature, density, composition, for an object that is modestly absorbing to the radiation used for measurement, and where the desired resolution is much larger than a radiation wavelength.